Rossby Vortices in Thin Magnetized Accretion Discs

We study the Rossby wave instability (RWI) in a thin accretion disc threaded by an initially toroidal magnetic field using the magnetohydrodynamics (MHD) code PLUTO. We find that for plasma \(10^1 < \beta < 10^3\) , the growth rate and late-time density are suppressed, whereas for plasma \(\beta > 10^3\), the magnetic field has negligible effect. The initially toroidal field is twisted inside the vortex and expelled at late times. This creates a radially directed field outside the vortex region, which can be understood via a simple kinematic model of a magnetic field in a rotating fluid and may be observable via polarised dust emission.